Lockheed Martin shrinks the telescope

After 400 years, the original telescope design is getting a major upgrade. Part of a DARPA funded project, Lockheed Martin's Segmented Planar Imaging Detector for Electro-optical Reconnaissance (SPIDER) telescope replaces the large primary lenses used in refracting telescopes with an array of tiny ones that allow the instruments to shrink by a factor of 10 to 100.

The basic design of the refracting telescope has remained essentially the same since its invention in 1608. At the front is a large lens like that of a magnifying glass that gathers in light and feeds it to a smaller lens that turns it into an image. Though there have been many refinements over the centuries, such telescopes have been hampered by the fact that in order to make a refracting telescope more powerful, the front or primary lens needs to be larger and therefore heavier.

The problem is that grinding optical lenses is a slow, precise process and in large telescopes it can take years to finish one. What's worse, glass lenses tend to sag under the force of gravity, are opaque to certain wavelengths, and are prone to residual chromatic and spherical aberration. Small wonder that the largest refracting astronomical telescope is still the Yerkes Observatory's 100-cm (40 in) scope competed in 1895.

Cross cut view of a SPIDER array(Credit: Lockheed Martin)

Developed by Lockheed Martin's research partners at University of California, Davis, SPIDER replaces the primary lens with a thin array of tiny lenses like the eye of an insect. Each of these lenses feeds light to a silicon-chip photonic integrated circuits (PIC), so the telescope is essentially a bank of still cameras.

The clever bit is that SPIDER operates on the principle of interferometry. Normally, this is used by astronomers as a way of turning a number of optical or radio telescopes distributed across an area into one gigantic telescope. It does this by combining the images from these telescopes so they interfere with one another. By analyzing the amplitude and phase of the interference patterns, scientists can turn them into a new image of much higher resolution.

Lockheed is using this principle to make a much smaller and lighter telescope that can be carried on a spacecraft.

Exploded view of a SPIDER array(Credit: Lockheed Martin)

"What's new is the ability to build interferometer arrays that have the same number of channels as a digital camera," said Alan Duncan, senior fellow at Lockheed Martin. "They can take a snapshot, process it and there's your image. It's basically treating interferometer arrays like a point-and-shoot camera."

Lockheed says that SPIDER's tiny lenses and PICs mean that construction doesn't require the elaborate grinding or alignment work of conventional lenses. While to achieve the same performance as a 40-inch telescope lens the SPIDER array would have to be the same diameter, it would be very thin by comparison, resulting in a 99 percent savings in cost and weight, and construction measured in weeks instead of years. In addition, a SPIDER telescope doesn't have to be a tube. As a flat disc, it can be any number of shapes from a circle to a hexagon and can be molded to fit a particular surface.

Currently, SPIDER is in the early stages of development and it may be five to ten years before it finds its first applications.

"SPIDER has the potential to enable exciting discoveries by putting high-resolution imaging systems within outer planet system orbits such as Saturn and Jupiter," says Duncan." The ability to reduce size, weight, and power could significantly change the game. With 10 to 100 times the resolution of a comparable-weight traditional telescope, imagine what you could discover."